1. Field of the Invention
This invention relates to a fuel injector for use in internal combustion engines, and more particularly to an accumulator type fuel injector.
2. Description of the Prior Art
Fuel injection through injectors having a spring biased or loaded nozzle valve capable of opening inwardly has been much improved by the provision of a fuel accumulator chamber formed within the injector body.
Fuel injectors of accumulation type have so far been developed. For example, in the specification of U.S. Pat. No. 2,959,360 by William M. Nichols, there is disclosed a fuel injector having a spring loaded nozzle valve capable of opening inwardly and a fuel accumulator chamber formed within the body thereof. Further, a similar fuel injector is disclosed in Japanese uitlity model application laid-open publication (provisional publication) No. Sho 56-94854 provisionally published on July 28, 1981. These fuel injectors are constructed such that, upon completion of the supply of fuel under high pressure into an accumulator chamber, a spring loaded needle valve is moved by the fuel under high pressure against the force of the spring to allow the fuel under high pressure within the accumulator chamber to be injected through injection orifices into the combustion chamber of the engine.
The above-mentioned fuel injectors have however been disadvantageous as mentioned below since the volume of an accumulator chamber formed in their bodies is always kept constant. Stating briefly, fuel under a predetermined high pressure is supplied by a Bosch type fuel injection pump etc. at a volume proportional to the load on the engine into the accumulator chamber so that when the engine is running at a high load, a large quantity of fuel under high pressure can be supplied into the accumulator chamber, whilst when the engine is running at a low load, a small quantity of pressurized fuel can be supplied into the accumulator chamber. Accordingly, when the engine is running at a high load, the pressure in the accumulator chamber rises rapidly with the result that the needle valve will move quickly, because the volume of the accumulator chamber is always kept constant. Whilst, when the engine is running at a low load, the pressure within the accumulator chamber rises slowly, and therefore the needle valve will move slowly by the same reason.
As described above, it is not preferable that the timing of injection of fuel under high pressure through injection orifices of the fuel injector into the combustion chamber of the engine varies depending on the load on the engine. Further, in such a case, when the quantity of fuel under high pressure supplied into the accumulator chamber is minimum, it is not always possible to actuate the needle valve properly, and in many cases it becomes difficult to obtain a minimum amount of fuel to be injected into the combustion chamber of the engine.